The present invention relates to footwear and more particularly to footwear constructions and methods for manufacturing footwear.
There is a wide variety of constructions used by the footwear industry to form footwear. In many cases, the construction used for a specific article of footwear is selected based on the intended use of the footwear. For example, some sole constructions are selected for their durability, others for their flexibility and comfort, while still others are selected for their aesthetic appeal. One particularly popular type of sole construction is referred to as a welt construction. Welt constructions are popular because they are durable and are aesthetically desirable. There is a variety of different types of welt constructions, but in a typical construction a “welt,” for example, a strip of material such as leather or hard rubber, is used to intersecure the sole and the upper. The welt extends around the article of footwear at the seam between the upper and the sole, and is secured to both the upper and the sole to indirectly join the two. In a traditional welt construction, the upper is closed by an insole having a downwardly extending rib, and the welt is attached to upper by stitching (or staples) that extends through the upper and the insole rib. This forms an upper/insole assembly that may be attached to the sole. Referring again to a traditional welt construction, a midsole is attached to the upper/insole assembly by stitching (or staples) that extends through the welt and the midsole. Afterwards, an outsole is secured to the bottom of midsole, typically by an adhesive.
To improve the flexibility and reduce the weight of the sole, a variety of welt constructions have been developed which incorporate a polyurethane (“PU”) outsole that is direct attached to the undersurface of the midsole. Although available in a broad range of densities, PU is generally a relatively soft material and it is not as wear-resistant as many other outsole materials, such as leather and rubber. To extend its life, a direct-attach outsole is typically manufactured from high density PU. High density PU has improved durability, but suffers from certain disadvantages. For example, high density PU is heavier and stiffer than low density PU. Accordingly, its use can result in footwear that is both stiffer and heavier. As another example, high density PU may have a greater tendency to crack and separate from the midsole under the stress of repeated flexing during use. Experience has shown that this tendency worsens with thicker PU components. Accordingly, manufacturers that wish to use direct attach outsoles are typically faced with a choice of balancing various advantages and disadvantages.